Telephone exchange system



Sept. 15, 1931.

TWO 5 TEP H. HOVLAND' 1,823,688

TELEPHONE EXCHANGE SYSTEM Filed June 2a. 1922-; 2 sheets-sneer 1 2-5 2/T MAAGM/AL DUUUUDUU /N I/EN 717/? H. HUI LAND Sept. 15, 1931.

H. HOVLAND 1,823,688

TELEPHONE EXCHANGE SYSTEM Filed June 28, 1929 2 Sheets-Sheet 2 Pom/wPatented Sept. 15, 1931 NET-E STATES HENRY HOVLAND, OF WILLISTON PARK,NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEWYORK, N. Y., A CORPORATION OF NEW YORK TELEPHONE EXCHANGE SYSTEMApplication filed June 28,

This invention relates to telephone systems and more particularly toparty-line message registration in automatic telephone systems.

The object is to enable the performance of a more positive and reliabletest of partylines to identify the station originating the call.

According to this invention, means are provided for testing a party-lineto determine which of the parties has originated the call, the testbeing made immediately after the calling subscriber has dialed the firstdigit of the called stations number. By making the test at this time thepossibility of a false determination on account of the removal of thereceiver at another station on the line is eliminated. The drawings,comprising Figs. 1 and 2,

6 disclose a portion of a step-by-step automatic telephone system inwhich this invention is embodied.

Fig. l diagrammatically represents a linefinder circuit LF and twosubscribers sta- 5 tions A and B, one of which is assumed to be acalling station. The stations A and B are connected by the line 1 toterminals in the bank of the line-finder switch LF and to terminals inthe banks of other line-finders in the same group with LF. The subscrilrers set at station A is arranged so that ground is connected to the linewhen the receiver is removed from the receiver-hook to originate a calland the subscribers set at station E is arranged so that ground is notsoconnected. Two message reglsters are shown associated with the line 1,one for each of the stations A and B. The group relay 4 is common to agroup of lines in- 40 cluding the line 1; the starting conductor 5connects to the first of a plurality of linefinders each of which hasaccess to the line 1. During the time that a line-finder is engaged, thestarting conductor is extended to the next idle line-finder in the samegroup.

The line-finder switch LF, which is of the well known Strowger type,includes a com mutator whose segments correspond to the groups of linesto which the line-finder has an access; the associated commutator'brush15 19589. Serial No. 374,358.

is carried by the shaft of the line-finder switch so as to make contactwith a given segment of the commutator while the multiple brushes 11 tolet inclusive are positioned at the corresponding level of the multiplebank.

Fig. 2 diagrammatically represents a trunk circuit T, a selector circuitS, a connector circuit C, a subscribers station D, and an operatorsposition 0. The trunk circuit T, which is individual to the line-finderLF, shown in Fig. 1, andto the selector S is arranged to test the lineof the calling subscriber, immediately after the first digit of thecalled subscribers number has been dialed, to determine which of the twosta tions associated with the line has originated the call. The trunkcircuit T is also arranged to operate the calling subscribers messageregister if a talking connection is established between the calling andcalled stations and the call is one for which the calling subscribershould be charged. The selector S has access to groups of trunks, eachtrunk terminating at a connector switch or an operators position; thebrushes 71 to 74 inclusive of the selector switch are shown in contactwith terminals which are connected to the connector circuit C. Theconnector C, which is represented by the brushes 81, 82 and 83, hasaccess to groups of lines, one of which includes the line 100 whichterminates at the subscribers station D; the brushes of the'connectorswitch are shown in contact with the terminals of the set to which theline 100 is connected. The operation of the circuit shown in Figs. 1 and2 will now be described in detail. Assume that a call is originated bythe removal of the receiver from the receiver hook at either of stationsA or B, and that the called station is the station D. The line relay 2,which is thereupon energized in an obvious circuit, closes a circuit foroperating group relay 4. In operating, relay 4' connects ground to thestarting conductor 5 and also connects ground over group conductor 6 tothe commutator segment, of each of the linefinders associated withthestart'ing conductor 5, corresponding to thegroup of multiple bankterminals which include the set of terminals connected to line 1. Asshown in Fig l, conductor 6 is connected to the second commutatorsegment of line-finder switch LF and it follows therefore that the setof multiple bank terminals, to which the line 1 is connected, is locatedin the second group (level) of the multiple bank.

Assuming that the line-finder LF is idle at the time that relay 4operates, a circuit is closed from battery through the winding ofslow-to-release relay l6, normally closed contacts of the10th-rotary-step springs, and through the normally closed contacts ofthe continuity spring combination of relay 18, to ground over startingconductor 5. Relay 16 operates, thereby closing a circuit for operatingstepping relay 17 this circuit may be traced from ground through theinner left-hand front contact of relay 16, through conductor 25, backcontact of the vertical stepping magnet 21, back contact of the rotarystepping magnet 22, right-hand winding of relay 17 and through the outerlefthand back contact of relay 18, to battery.

' Relay 17 closes a circuit for energizing vertical stepping magnet 21;this circuit may be traced from the ground at relay 16 over conductor25, through the front contact of relay 17 inner right-hand back contactof relay 19, winding of vertical stepping magnet 21,

and through the outer left-hand back contact of relay 18, to battery. Inenergizing,

the magnet 21 opens the circuit through the right-hand winding ofstepping relay 17 and steps the shaft, carrying the multiple brushes 11,12, 13 and 14 and the commutator brush 15, up one step to the firstlevel. The release of relay 17, when the magnet 21 operates, opens thecircuit through the winding of the stepping magnet 21. The release ofmagnet 21 closes the circuit through the right-hand, winding of steppingrelay 17. The alternate operation and release of magnet 21, ascontrolled by stepping relay 17, is

eflective to raise the shaft of the line-finder switch step-by-step.When raised to the level at which the commutator brush 15 is in contactwith the group segment to which group conductor 6 connects, a circuit isclosed from the ground at group relay 4 over conductor 6, throughcommutator brush 15, right-hand winding of relay 19, back contact ofmagnet 22, right-hand winding of relay 17, and through the outerleft-hand back contact of relay 18, to. battery. The closing of thiscircuit prevents the release of relay 17 and causes the operation ofrelay 19. In operating,'relay 19 opens the circuit through the windingof vertical stepping magnet 21 so that magnet 21 releases. Relay 19closes a circuit from battery through the outer left-hand back contactof relay 18, winding of vertical stepping magnet 21, left-hand windingand front contact of relay 19, over conductor 25 to ground at relay 16.The current in this circuit is not strong enough to operate the magnet21 but is effective to hold relay 19 after the rotary movement of theswitch has opened the circuit through the right-handwinding of thisrelay at the commutator brush 15.

The aforementioned operation of relay 19 also closes a circuit foroperating the rotary stepping magnet 22; this circuit may be traced frombattery, through the winding of the rotary stepping magnet 22, innerright-hand front contact of relay 19, front contact of relay 17, andconductor 25, to ground at relay 16. The operation of rotary magnet 22opens the circuit through the right-hand winding of stepping relay 17and relay 17 releases. The release of relay 17 opens the circuit throughthe winding of the magnet 22 and the release of magnet 22 closes thecircuit for operating relay 17. The alternate operation and release ofthe rotary stepping magnet 22, as controlled by stepping relay 17, iseffective to rotate the shaft and brushes of line-finder LF step-bystepso that the multiple brushes 11 to 14: inclusive successively makecontact with the sets of terminals in the previously selected level.When the sleeve brush 13 makes contact with the terminal associated withthe line 1 a circuit is closed from battery through the windings of thecutoff relay 3 and the message register 7 in parallel, front contact ofrelay 2, over lead 9, through brush 13, lower winding of'relay 20,righthand back contact of relay 18, left-hand winding of relay 17, andover lead 25 to ground at relay 16. The current in this circuit iseifectiveto operate the cut-off relay 3, to prevent the release of relay17 and to close the inner upper front contact of relay 20. The messageregister 7 is marginal and does not operate at this time. Since relay 17does not release the rotary magnet 22 remains operated and a circuit 110for operating the remaining contacts of relay 20 may be traced frombattery through the upper winding and front contact of relay 20, frontcontact of magnet- 22, conductor 28, and through the outer lefthand 115front contact of relay 16, to ground. In case the sleeve brush 13 passesover the grounded sleeve terminal of a busy line the opening of thecircuit through the righthand winding of relay 17 may induce sufli- 1 20cient current in the circuit through its lefthand winding to cause theoperation of relay 20 (this circuit may be traced from ground at thesleeve terminal of the busy line, through the lower winding of relay 20,125 right-hand back contact of relay 18, lefthand winding of relay 17,and over conductor 25, to ground at relay 16). In this case the releaseof the rotary magnet 22 prevents the complete operation of relay 20.

The aforementioned complete operation of relay 26 connects the tip andring brushes of the line-finder to the tip and ring conductors 26 and 27of the trunk T and closes a circuit for operating relay 18. This circuitmay be traced from battery through the right-hand winding of relay 18,through the outer upper front contact of relay 20 and through the upperfront contact of the vertical off normal springs V. O. N. These springswere actuated when the line-finder shaft was moved out of its normalposition. In operatin relay 18 opens the circuit through the lowerwinding of relay 20 and extends the connection, from the sleeve brush 13of the line-finder switch tl'irough the lower front contact of relay andthe outer ri sleeve conductor 28 of the trunk T. The closing of theinner right-hand front contact of relay 18 renders the circuit throughthe locking winding and front contact of relay 26 independent of thecontinued operation of rotary stepping magnet 22. The opening of theouter left-hand back contact of relay 18 disconnects battery from thewinding of the vertical magnet 21 and from the right-hand winding ofrelay 17 thus causing the release of relay 17 and relay 19. Theoperation of relay 18 disconnects the starting conductor 5 from thewinding of relay 16, and connects conductor 5 through its left-handfront contact to its left-hand winding. lVith relay 18 operated andrelay 19 released the starting conductor is further extended through theleft-hand front contact of relay 18 and the middle righthand backcontact of relay 19, over conductor 24 to the next line-finder whichhas: access to the same groups of lines to which the line-finder Ll hasaccess. The aforementioned operat on of cut-off relay 3 disconnects thewindings of line relay 2 from the line thus causing the release of relay2'. In operating, relay 3 connects its winding through its own frontcontact to sleeve conductor 9 so that the release of relay 2 does notcause the release of relay The group relay 4 releases unless a call hasbeen originated at a station connected to some other line in the groupof lines with which relay 4 is associated. The release of relay 4disconnects ground from starting conductor 5 and thus opens the circuitthrough the winding of relay 16 if not already opened by theaforementioned operation of relay 18. Relay 16 is slow in releasing toinsure the complete operation of relay 20 before the sleeve conductor 28is disconnected from the ground at the front contact of relay 16.

With the line-finder brushes lland 12 connected to the tip and ringconductors 26 and 27 of trunk T, as hereinbefore described, line relay30 of the trunk circuit T is operated. The circuit for operating relay3O ht-hand front contact of relay 18, to the may be traced from batterythrough its winding, through the back contact of the lower continuitysprings of relay 40, middle lower back contact of relay 39, conductor2-7, middle lower front contact of relay 20, line-finder brush 12, ringconductor of line 1, through the calling subscribers instrument, backover the tip conductor of line 1, through line-finder brush 11, innerlower front contact of relay 20, conductor 26, upper back contact ofrelay 39, back contact of the upper continuity springs of relay 40, andthrough retard coil 41, to ground. Relay 30 closes a circuit from groundthrough the inner upper back contact of relay 40, lower front contact ofrelay 30, lead 42, and through the Winding of relay 37 to battery. Relay37 operates thereby connecting ground through its inner left-hand, frontcontact over lead 43, through normally closed contacts of both sets ofcontinuity springs of relay 36, and through the normally closed contactsof the continuity springs of relay 33, to the sleeve conductor 28 of thelinefinder LF. After the release of relay 16 as hereinbefore described,the cut-off relay 3 and relay 20 are held in the circuit over conductor28 to ground at the contact of relay 37 Since relay 16 of theline-finder circuit is slow in releasing relay 37 is sure to operate andconnect ground to conductor 28 before the ground at the outer frontcontact of relay 16 is disconnected from this conductor.

The aforementioned operation of relay 3O closes a circuit for operatingthe line relay 61 of the selector S; this circuit may be traced frombattery through the left-hand winding of relay 61, inner upper backcontact of relay 64, ring conductor 57, righthand winding of polarizedsupervisory relay outer lower back contact of relay 40, lower backcontact of relay 32, retard coil 46, upper front contact of relay 30,outer upper back contact of relay 40, left-hand winding of relay 55, tipconductor 56, outer upper back contact of relay 64, right-hand windingof relay 61, upper back contact of the 11th rotary-step springs, toground. The line relay 61 closes a circuit from battery through thewinding of relay 62, front contact of relay 61, conductor 7 O,andthrough the outer lower back contact of relay 64, to ground. Relay 62operates, thereby connecting ground through its right-hand front contactto the sleeve conductor 59 of the trunk T.

The afore-inentioned operation of relay 30 also closes a circuit foroperating relay 31; this circuit may be traced from battery through thewinding of relay 31, back contact of relay 35, resistance 44, outerleft-hand back contact of relay 38, lead 42, lower front contact ofrelay 30, and through the inner upper back contact of relay. 40, toground.

Ian

' 33 locks through its inner righthand Relay 31 closes a circuitfor 33,which may be traced from battery, through the winding of relay 33, frontcontact of relay 31, and through the inner lower back contact of relay40, to ground. Relay front contact, through the outer right-hand backcontact of relay 38 in parallel with the lefthand back contact of relay34, lead 45, and through the outer left-hand front contact of relay 37,to ground. In operating, relay 33 closes a circuit, for operating relay38, which operating relay may be traced from battery through the windingof relay 38, outer right-hand front .contact of relay 33. over sleevelead 59,

to ground at relay 62 of selector S. Relay 38 locks through its innerleft-hand front contact to the ground on sleeve lead 59. In operating,relay 38 causes the release of relay 31 and closes an obvious circuitfor holding relay 37 The circuit through the winding of theidentification test relay 31 was closed as hereinbetore described, so asto be sure that this relay is in condition to determine which of thestations on the calling line has originated the call, when theidentification test circuit is closed as hereinafter described. Shouldrelay 38 fail to operate at this time the ground connected through theinner right-hand front contact of relay 37 and the inner left-hand backcontact o1 relay 38 is effective to operate alarm circuit 51. Althoughthe call may be completed, the charge control relay is not operated andthe charging circuit is not closed when the connection is released.

lVhen the subscriber at the calling station dials the first digit of thenumber of the called station the line relay 30 of trunk T is alternatelyreleased and reoperated each first digit of the time the subscribersline and closed at the dial. Each release and reoperation of relay 30opens and closes the bridge through the retard coil 46 (across the tipand ring conductors 56 and 57 of the trunk to the selector S) andtheline relay 61 of selector S is alternately released and reoperated inresponse to the dialing ofthe called number. The release of line relay30 of trunk T closes a circuit, for operating relay 32, from batterythrough the winding of relay 32, outer right-hand front contact of relay37, back contact of relay 30, and through the inner upper back contactof relay 40 to ground. Relay 32 is slow to release and remains operateduntil all of the impulses created by the dialing of the first digit havebeen received. In operating, relay 32 short-circuits the winding of theretard coil 41, thus reducing the impedance of the dialing loop, andalso shortcircuits the windings of the retard coil 46 and resistance 47to reduce the impedance of the trunk loop to the windings of the line.

loop is opened relay 61 of selector S. At the end of the train ofimpulses relay 30 reoperates and relay 32 releases. Resistance 47 isconnected from the armature to the back contact of relay 32 to preventthe opening and closing of the trunk loop when relay 32 releases. Relay37 is slow to release and holds during the receipt of each train ofpulses which are originated by the dialing of the digits of the calledstations number.

When the line relay 61 of selector S releases, a circuit is closed frombattery, through the winding of the vertical stepping nagnet 66, windingof relay 63, left-hand front contact of relay 62, back contact of relay61, conductor 70, and through the outer lower back contact of relay 64,to ground. The magnet 66 and relay 63 both operate in this circuit.Relay 63 is a slow-to-release relay and remains operated until all ofthe impulses corresponding to the first digit have been received. Relay62 is also slow to release and holds during the receipt of this train ofimpulses. The operation of magnet 66 steps the shaft and brushes ofselector S up to the first level of bank terminals. The reoperation ofline relay 61 releases the magnet 66, and each successive release andreoperation of relay 61 causes the operation and release of magnet 66.The shaft and brushes of the selector are in this manner raised,step-by-step, to the level through which the call may be eX- tendedtoward the called station.

As soon as the shaft of selector S is moved oil normal the vertical offnormal springs V. O. N. are actuated and when relay 63 operates, ashereinbefore described, a circuit is closed, for operating relay 65,from battery through the winding of relay 65, upper contact of the V. O.N. springs, front contact of relay 63, and over sleeve conductor 59, toground at relay 62. Relay 65 locks in a circuit from battery through itswinding and the upper contact of the V. O. N. springs, through the backcontact of the rotary stepping magnet 67, conductor 69, lefthand frontcontact of relay 65, and through the outer lower back contact of relay64 to ground. The operation of relay 63 is also effective to connectground from sleeve conductor 59 through a front contact of relay 63 toconductor 60 and thus cause the operation of relay 34 of the trunkcircuit T. Relay 34 locks through its left-hand front contact, normallyclosed contacts of the continuity springs of relay 39, and through theright-hand back contact of relay 36, over conductor 45, to ground atrelay 37. The operation of relay 34 causes the release of relay 33.

WVhen all of the impulses, originated by the dialing of the first digitof the called number have been received, the release of relay 63 ofselector S disconnects the ground over sleeve conductor 59 fromconductor 60; and the release of relay 32 of trunk T closes a circuit,for operating relay 39, from battery through the winding of relay 39,right-hand front contact of relay 34, and through the upper back contactof relay 32, to ground. In operating, relay 39 (a) trans fers the tipand ring conductors 26 and 27 from the windings of relay 30 and retardcoil 41 to the winding of identification test relay 31, (b) closes acircuit, for holding line relay 30, from battery through the winding ofrelay 30, resistance 50, inner lower front Contact of relay 39, innerleft-hand front contact of relay 38, over sleeve lead 59, to ground atrelay 62 of selector S, and (0) opens the locking circuit of relay 34.Relay 34 releases since its operating circuit, over lead 60, has beenopened by the release of relay 63 of selector S. The release of relay 34causes the release of relay 39 whereby the conductors 26 and 27 areagain connected to the windings of line relay 30 and retard coil 41. Therelease of relay 39 also disconnects the winding of identification testrelay 31 from conductors 26 and 27.

1f the call originated-at station A, the identification test relay 31operates during the time that its winding is connected over conductors26 and 27 through the front contacts of relay 20, line-finder brushes 11and 12 over the tip and ring conductors of line 1 to the identificationground 10 at the instrument of station A. If the call originated atstation 13, relay 31 does not operate for there is no identifying groundconnection at station B. If relay 31 operates relay 33 operates; andrelay 33 locks through its inner right-hand front contact and theouterleft-hand back contact of relay 34, over lead 45 to'ground at relay37. Relay 33 controls the message register operating circuit so that theregister which corresponds to the calling station is operated, ashereinafter described, when a completed call, for which a charge is tobe made, is released by the calling subscriber.

The release of relay 63 ofselector S, after the dialing of the firstdigit, is also effective to close a circuit for operating the rotarystepping magnet 67; this circuit may be traced from battery through thewinding of magnet 67, left'hand front contact of relay 65, normallyclosed contact of relay 63, over sleeve conductor 59, to ground at relay62. The rotary magnet 67 rotates the shaft of selector S one step, sothat the brushes 71, 72, 73 and 74 make contact with the terminals ofthe first trunk in the previously selected level. The operation of therotary magnet causes the release of relay 65. The release of relay 65causes'the release of the rotary magnet. The release of magnet 67 closesa circuit from battery through the winding of relay 65, upper contact ofthe V. O. N. springs, back contact of magnet 67, conductor 69, windingof relay 64, lower contact of the llth-rotary-step springs, overconductor 59 to ground at relay 62. Conductor 69 is also connectedthrough the inner lower back contact of relay 64 and the sleeve brush 73to the sleeve terminal of the first trunk in the selected level. If thistrunk is idle relay 64 operates and relay 65 does not operate; but ifthe trunk is busy the winding of relay 64 is short-circuited so thatrelay 65 operates and relay 64 does not operate. The reoperation ofrelay 65 causes the reoperation of the rotary stepping magnet 67. Thealternate'operation and release of relay 65 and magnet 67 advances thebrushes of selector S step-by-step from one set of terminals to thenext.

hen an idle trunk is encountered relay 64 operates, therebydisconnecting thetip and ring conductors 56 and 57 from the windings ofline relay 61 and extending these conductors through brushes 71 and 72over the tip and ring conductors of the selected trunk to the windingsof the line relay (not shown) of connectorC. Relay 64 also establishes atemporary busy condition on the test terminal of the selected trunk byconnecting the sleeve conductor 59 through the inner lower front contactof relay 64 to the sleeve brush 73. Relay 61 releases'thereby causingthe release of relay 62. Relay 62 is slow to release so that the groundat its left-hand front contact is not disconnected from sleeve conductor59 until suflicient time has elapsed for the operation of the line relay(not shown) of connector C to have been effective to cause a permanentbusy ground to be connected through brush 73, and the inner lower frontcontact of relay 64, to sleeve conductor 59.

hen the remaining digits of the called stations number are dialed by thecalling subscriber, line relay 30 and slow-to-release relay 32 of trunkT repeat the impulses over i the trunk conductors 56 and 57 through theselector circuits S, to the line relay (not shown) of the connector C.The connector C is thus controlled to select the terminals of the line100 of the called station. For a detailed explanation of the operationof the connector circuit reference may be had to pages 57 to 61inclusive of the second edition of Automatic Telephony by Smith 1 andCampbell.

Assume that the line 100 is idle, when connectionis establishedtherewith, that ring ing potential is connected to the line, that thesubscriber at the called station answers,

and that the call is one for which the calling 1 subscriber should becharged. YVhen the receiver is removed from the receiver hook at thecalled station, the windings of the line relay (not shown) of theconnector C are reversed, inthe usual manner, with respect to the tipand ring conductors 56 and 57 of the trunk T; and as a result thecurrent through the windings of the polarized supervisory relay 55 is inthe direction to operate this relay. The circuit for operating relay 55may be traced from battery through one winding of the line relay (notshown) of the connector C over the tip conductor, through brush 71,outer upper front contact of relay 64, conductor 56, left-hand windingof relay 55, outer upper back contact of relay 40, upper front contactof relay 30, retard coil 46, lower back contact of relay 32, outer lowerback contact of relay 40, right-hand winding of relay 55, conductor 57,inner upper front contact of relay 64, brush 72, over the ring conductorand through the other winding of the line relay (not shown) of connectorC, to ground. The talking circuit may at this time be traced from trunkconductors 26 and 27 through condensers 48 to the trunk conductors 56and 57 which connect to the selector S.

The operation of the supervisory relay 55 closes a circuit for operatingrelay 35; this circuit may be traced from battery through the winding ofrelay 35, front contact of relay 55, and through the right-hand frontcontact of relay 38, to ground. Relay 35 locks through its right-handfront contacts, over lead 45 to ground at relay 37. Relay 35 closes anobvious circuit from the ground at relay 37 over leads 45 and 49 foroperating relay 40. Relay 4O disconnects the windings of the line relay30 and retard coil 41 from trunk conductors 26 and 27 and disconnectsthe retard coil 46, resistance 47 and condensers 48 from trunkconductors 56 and 57. Relay 3O releases and the talking circuit is nowtraced directly from conductors 26 and 27, through the back contacts ofrelay 39, front contacts of relay 40, and windings of supervisory relay55 to conduc tors 56' and 57. The line relay (not shown) of connector Cisheld operated in the circuit which includes the calling line until thecalling subscriber releases the connection.

When the calling subscriber replaces the receiver on the receiver hook,the line relay (not shown) of connector C releases. The connectorswitch. is returned to normal in the usual manner. When the sleeveground at connector C is disconnected from the sleeve terminal withwhich brush 73 is in contact, relay 64 of selector S and relay 38 oftrunk T are both released. The release of relay 64 closes a circuit foroperating the release magnet 68 and selector S is returned to normal inthe usual manner. In releasing, relay 38 closes a circuit for operatingrelay 34; this circuit may be traced from battery through the winding ofrelay 34, conductor 60, inner left-hand front contact of relay 35,middle right-hand back 0011- tact of relay 38, conductor 49, outerrighthand front contact of relay 35, and over conductor 45, to ground atrelay 37. Relay 34 closes again the circuit for operating relay 3 Relay37 is slow in releasing so that it holds, after relay 38 releases, untilrelay 39 operates. Relay 39 prevents the release of relay 37 by closinga holding circuit which may be traced from battery through the windingof relay 37, outer lower front contact of relay 39, right-hand backcontact of relay 36, and over lead 45, to ground at relay 37. Theoperation of relay 39 transfers the connection from the calling line,over conductors 26 and 27 to the winding of test relay 31. Since thecalling subscriber has hung up the receiver test relay 31 fails tooperate unless ground has been falsely (or otherwise) connected to theline. If relay 31 operates, the operation of relay 36 is prevented forrelay 36 is slow in operating. In this case the line-finder does notrelease and the ground connected, through the inner right-hand frontcontact of relay 37 and the inner left-hand back contact of relay 38, iseffective to operate the alarm circuits 51. If relay 31 does notoperate, relay 36 operates in a circuit which may be traced from batterythrough the winding of relay 36, back contact of relay 31, inner upperfront contact of relay 39, inner righthand back contact of relay 38, andover conductor 43 to ground at relay 37. Relay 36 closes the circuit foroperating the calling subscribers message register.

If the call originated at station A the charging circuit is traced frombooster bat- .tery 52, through lamp 53, resistance 54, middle left-handfrontcontact of relay 35, outer left-hand front contact of relay 36,outer left hand front contact of relay 33 (relay 33 having beenoperated), conductor 29, linefinder brush 14, and through the winding ofmessage register 8, to battery. If the call originated at station B thecharging circuit is traced from the booster battery through the normallyclosed contacts of the continuity springs of relay 33 (relay 33 nothaving been operated), over sleeve conductor 28, outer right-hand frontcontact of relay 1.8, outer lower front contact of relay 20, line finderbrush 13, conductor 9, and through the windings of the cutoff relay 3and message register 7 in parallel, to battery. Relay 36 connects groundthrough its righthand front contact to conductor to hold relay 34. Thisground connection is extended from conductor 60 through the innerlefthand front contact of relay 35 and the middle right-hand backcontact of relay 38, to conductor 49 thereby holding relays 35 and 40.If relay 33 has been operated, relay 36 also connects ground through theinner lefthand front contacts of relays 36 and 33 to the sleeveconductor 28, in place of the ground over conductor 43 so as to preventthe release of the line finder LF until the register 8 has beenoperated. Relay 36 opens the holding circuit for relay 37. The releaseof relay 37 causes the release of relays 33 and 36. The release of relay36 causes the release of relays 34:, 35 and a0. The release of relay 3dcauses the release of relay 39. Since relay 37 is slow-to-release thecharging circuit is closed for a sullicient length of time to insure theoperation of the calling subscribers register. The release of relay 37causes the release of line-finder relay 2O andcut-ofl relay 3.Therelease of relay 2O closes the circuit for operating the line-linderrelease magnet 23 thereby causing the line linder to be restored tonormal. Relay 18 releases when the line-finder switch reaches its normalposition unless the starting conductor 5 is connected to ground by theoperation of one or more of the group relays such as d. In this eventanother linefinder is being started to find a calling line and relay 18holds to prevent the operation of relay 16.

If the first digit dialed by the calling subscriber is such that theselector S seizes an idle trunk leading to an operators position, theterminal with which the brush 7 a makes contact is grounded; terminal 78which is associated with the trunk 80 which leads to the operatorsposition 0 is, therefore, connected to ground as indicated. When relay64 operates this ground is connected through brush 74, lower frontcontact of relay 6st, conductor 58, and through the right-hand backcontact of relay 3et, to the winding of relay d0. Relay 10 operatesthereby extend ing the connection from the calling line over trunkconductors Q6 and 27 to trunk conductors 56 and 57 and through thebrushes of selector S to the trunk leading to the op erat rs position.Talking battery is supplied to the calling station from the operatorsposition; and the current through the windings of the polarizedsupervisory relay 55 is not ellective to operate relay 55 unless thecall is furt er extended by the operator, in which case 1e operator may.reverse the battery connected to the trun so as to operate relay 55. Insuch a case the message register of the calling subscriber is operated,in the manner hereinbetore described, when the connection is released bythe calling subscriber.

It a call is completed to a subscriber and is supplied to the callingstation through the windings of the line relay 30 and retard coil 41.When the connection released, relay 30 releases thereby opening thebridge across the trunk conductors 56 and 57 to release the line relay(not shown) of connector G. hen the sleeve ground at connector C isdisconnected. l 38 releases. The release of relay 3% causes the releaseof relay 37, and disco nects ground from conductor 43 thereby causingthe re turn of the line-finder LF to normal in the same manner ashereinbefore described.

The invention is not limited to a system using Strowger type switchesbut is appli- I cable to all systems in which the line of a callingsubscriber is extended in response to the eperationof an impulsetransmitter at the calling station and which are arranged formessage-rate party-line service.

What is claimed is:

1. In a telephone system, a line having a plurality of subscribersstations each of which possesses a distinguishing character,

line having a plurality of subscribers stations one of which is a.calling station, means for distinguishing each of said stations from theothers, an impulse sender at said calling station, means for receivingimpulses originated by the operation of said impulse sender, means forconnecting said calling line to said impulse receiving means, and meansrendered efiiective by the receipt of a series of impulses for testingthe calling line to determine which of said stations is the callingstation.

3. In an automatic telephone system, a line having a plurality ofsubscribers stations one of which is a calling station, means fordistinguishing each of said sta tions from the others, a calling deviceat said calling station, an automatic switch, means for extending saidline to said automatic switch, means for selectively actuating saidautomatic switch in response to impulses originated by the operation ofsaid calling device, aud means rendered effective immediately aftersaidswitch has responded to a ot'impulses for testing the calling lineto determine which of said stations is the calling station.

4. in a telephone system, a line, a pluraL ity of subs ribers stationspermanently cons nect-ed to said line, an identifying connection at oneof said stations, an impulse transmitter at each of said stations, amessage register for each of said. stations, an auto matic switch, meansfor extending said line to said switch upon the origination of a call atone of said stations, means for selectively actuating said automaticswitch in response to impulses originated by the operation of saidimpulse transmitter, means rendered effective by the receipt of a trainof impulses for testing said line to determine which of said stations isthe calling station, and means for operating the mes sage register oisaid calling station.

5. In a telephone system, a line, a plurality of subscribers stationspermanently connected to said line, an identifying connection at one ofsaid stations, a dial at each of said stations, a called station, anautomatic switch, means for extending said line to said switch upon theorigination of a call at one of said plurality of stations, meansincluding said switch controlled by the dialing oi the number of saidcalled station for establishing a connection between said calling andsaid called stations, and means ei fective during the interval betweenthe dialing of the first and second di its of the number of said calledstation for testing said line to determine which of said plurality ofstations is the calling station.

6. In a telephone system, a calling subscribers station, anothersubscribers station, a line common to both of aid stations, anidentifying connection at one of said stations closed upon theorigination of a call at said one of the stations, a dialing device atsaid calling station, a called stat-ion, means selectively actuated bythe dialing oi the number of said called station for establishing aconnection between said calling and said called stations, and meansconnected to said line during the interval between the dialing of two ofthe digits of the number of said called station for determining thepresence or al sence of said identifying connection.

7. In a telephone system, a calling subscribers station, anothersubscribers station, a line common to both of said stations, means atone of said stations for distinguishing it from the other of saidstations, a dial at said calling station, a called station, a trunk,means eifective upon the origination of a call ateither of said stationsfor extending said line to said trunk, means controlled by the actuationof said dial for establishing a connection between said calling and saidcalled stations, and means effective immediately after the dialing of adigit of the number of said called station for determining whether saidcalling station is the station with which said distinguishing means areassociated.

8. In a telephone system, a line having a plurality of subscribersstations, distinguishing means at one of said stations, a dial at eachof said stations, a trunk, means effective upon the origination of acall at one oi":

said stations for extending said line to said trunk, means controlled bythe actuation of the dial at the calling station for further extendingthe connection from said line, and means etlective between successiveoperations of said dial for determining whether the calling station isthe one with which said distinguishing means are associated.

9. In a telephone system, a line having a plurality of subscribersstations each of which possesses a distinguishing characteristic, a dialat each of said stations, a message register for each of said stations,a called station, a trunk, means effective upon the origination of acall at one of said plurality of stations for extending said line tosaid trunk, an automatic switch which is inclividual to said trunk andwhich is selectively actuated in response to the dialing of a digit,means eilective immediately after the dialing of said digit fordetermining which of said plurality of stations is the calling station,means for completing the connection between said calling and said calledstations, and means for operating that one of said message registerswhich is individual to said calling station.

10. In a telephone system, a line having a plurality of subscribersstations each of which possesses an identifying characteris tic, a dialat each of said stations, a message register for each of said stations,a called station, a trunk, means effective upon the origination of acall at one of said plurality of stations for extending said line tosaid trunk, an automatic switch individual to said trunk, meansassociated with said trunk for receiving impulses originated by theoperation of the dial at said calling station, means associated withsaid trunk for repeating impulses, means effective immediatcly after thedialing of a digit for determining which of said plurality of stationsis the calling station, means for completing the connection between saidcalling and. said called stations, and means effective in the event thata talking connection is established between said calling and calledstations for disconnecting said impulse repeating means and foroperating that one of said message registers which is individual to saidcalling station.

11. In a telephone system, a line having a plurality of subscribersstations each of which possesses an identifying characteristic, a dialat each of said stations, an operators position arranged to feed talkingbattery to said calling station, a trunk, means ei'lective upon the oriination of a call at one of said stations for extending said line tosaid trunk, means associated with said trunk for receiving impulsesoriginated by the operationv of the dial at said calling station, meansassociated with said trunk for repeating impulses, means effective im-Ill)

